Oil recovery method for displacement rotary air compressor

ABSTRACT

The turbine oil used in a screw-type air compressor as a lubricant and sealant is mixed with approximately 40 percent trichlorofluoromethane, trichlorotrifluoroethane, or dichlorotetrafluoroethane to raise the specific gravity of the mixture above that of water. When the compressed air discharged from the compressor is cooled, moisture condenses and the entrained droplets of the oil mixture are precipitated and settle under the aqueous condensate so that the latter may be removed by overflow while the oil mixture may be returned to the compressor.

United States Patent Uratani June 4, 1974 OIL RECOVERY METHOD FORDISPLACEMENT ROTARY AIR COMPRESSOR Eiichi Uratani, Tokyo, Japan SumidaEquipment Industries, Inc., Tokyo, Japan Filed: Sept. 1, 1972 Appl. No.:285,872

Inventor:

Assignee:

Foreign Application Priority Data Mar. 29, l972 Japan 47-30686 U.S. Cl.55/29 Int. Cl B0ld 53/14 Field of Search 55/45, 29, 34, 32; 210/21.

References Cited UNITED STATES PATENTS H1968 Schmauch et al. 55/452/l97l Sasseui 2lO/l68 3,634,247 l/l972 Parker 252/58 OTHER PUBLICATIONSEffects of Refrigerants on Lubricating Oils" Lubrication, Vol. 47, No.7, Texaco, Inc., July 1961, pp. 78-80.

Primary ExaminerCharles N. Hart Attorney, Agent, or FirmHans Berman [57]ABSTRACT The turbine oil used in a screw-type air compressor as alubricant and sealant is mixed with approximately 40 percenttrichlorofluoromethane, trichlorotrifluoroethane, ordichlorotetrafluoroethane to raise the specific gravity of the mixtureabove that of water. When the compressed air discharged from thecompressor is cooled, moisture condenses and the entrained droplets ofthe oil mixture are precipitated and settle under the aqueous condensateso that the latter may be removed by overflow while the oil mixture maybe returned to the compressor.

7 Claims, 2 Drawing Figures OIL RECOVERY METHOD FOR DISPLACEMENT ROTARYAIR COMPRESSOR This invention relates to an oil recovery method for anair compressor, and more particularly, to a method of recovering oilused in the lubrication, cooling, and sealing of positive displacementrotary air compressors such as a screw type compressor or the like.

Generally, the removal of oil from compressed air and dehydrationthereof is required before the use of such compressed air since thecompressed air discharged or exhausted from the compressor contains thecompressor lubricating oil and water therein. The currently and widelyavailable screw type compressor uses much oil for lubrication, cooling,and sealing thereby leaving much oil in the exhausted air. For thisreason, the problem of oil separation (or oil recovery) has beencritical. In the conventional screw type compressor, it has been thepractice heretofore that the air exhausted from the compressor is led tothe oil separator (or oil recovering device) in which the oil isseparated from the air, and then the separated and recovered oil as itis or cooled is returned to the compressor. However, this does notsatisfactorily remove all the oil from the air and the quality ofcompressed air is impaired for all the outstanding functions of thescrew type compressor. The compressed air thus obtained is restricted inuse and the compressor requires much consumption of oil. The oilreceovered and reused contains moisture which rusts the compressor. Inaddition, the compressor is not cooled sufficiently.

More specifically, anti-emulsifying oil is conventionally used in thescrew type compressor so that the oil finely divided as a mist iscarried in the exhausted air separately from the water. This allows theoil to readily pass along with the air through the oil separator. Infact, it has been found that capture of oil in the oil separator iscomplete if the exhausted air is cooled to form the finely divided oilinto relatively large droplets. However, this increases the condensationof water. Cooling of the compressor is also accompanied by an increasein the condensation of water. Water of condensation has a higherspecific gravity than that of oil and may lay under the layer of oil inthe oil separator to rust the compressor if this condensed water is fedalong with the air to the compressor and should the quantity ofcondensed water become large, it may lead to burning out of thecompressor due to poor lubrication. In this connection, separation ofwater from the oil and disposition of the water are necessary, but it isvery difficult to automatically discharge the water from under the oil.Thus the prior art apparently has failed to not only lower thetemperature of compressed air to be treated by the oil separator to anextent suitable for oil separation but also to cool down the compressorsufficiently.

Accordingly, it is an object of the present invention to provide amethod of recovering oil from the compressed air which allows both tolower the temperature of the compressor, oil and the exhaustedcompressed air sufficiently for protection of the compressor and removalof oil and also to completely separate the condensed water from therecovered oil and dispose of the water whereby eliminating difficulty inre-use of the recovered oil.

According to the invention, this object is accom plished by adding andmixing a proper material with the oil to be used to cause the oil toreach a higher specific gravity than that of water.

More particularly, when an additive material is mixed with the oil forlubrication of the compressor or for other purposes it properlyincreases the specific gravity of oil to more than that of water therebyreversing the normal specific gravity relationship between water andoil. Thus, in the oil separator the condensed water is supernatant over,and distinctly separated from, the recovered oil (normally the water isdeposited below the layer of oil). As a result, the condensed water isreadily and completely separated from the oil and disposed of byautomatically over-flowing the water. This prevents the water from beingmixed with the recovered oil to be reused so that the condensation ofwater makes no interference with the recover of oil. This enables thecompressor, oil and the exhausted compressed air to be cooledsufficiently enough for protection of the compressor and removal of oil.

The complete cooling of the compressor and removal of oil (or oilrecovery) above referred to increases the life-time of the compressorand makes it less costly to maintain the same and reduces theconsumption of oil and avoids acid deterioration of oil.

It should be noted that the method in accordance with the invention canbe carried out with utilizing the conventional installation andarrangement almost without modifying them.

FIG. 1 is a schematic representation showing a typical oil recoveryapparatus system for the compressor in which the conventional method iscarried out, and

FlG. 2 is a schematic representation showing a preferred oil recoveryapparatus system for the compressor in which a method according to thepresent invention is carried out.

Preferred properties of the aforementioned additive material are asfollows:

1. The boiling point of additive material under atmospheric pressure ishigher than the freezing point of water but lower than the boiling pointthereof. (The additive material should not be evaporated within thecompressed air.)

2. The solubility of additive material is high with respect to the oilbut is low with respect to the water (for the purpose of adding to theoil to be used and of facilitating its separation from the condensedwater.)

3. The additive material should be of high specific gravity (for thepurpose of adding to the oil to be used thereby causing the specificgravity of oil to be more than that of water.)

4. The additive material must have appropriate viscosity (to provide theoil with appropriate lubricant property.)

5. The additive material should be noninflammable, non-toxic, andanti-corrosive to machinery and tools.

The following compounds have been found to be suitable in carrying outthe invention as a result of various experiments in view of theaforementioned preferred properties of additive material.

Identification Chemical Name of as Refrigerant Formula Compound RI 1CCl;,F Trichlorofluoromethane R-l l3 C Cl l Trichlorotrifluoroethanethanc Preferred addition rates of these additive materials to the oil involume percent of the oil before mixing are as follows. The oil whichhas the additive material mixed at such rate, provides kinetic viscosityof 1 1-15- cst/30C and specific gravity of 1.lkg/ l.

Additive Oil in Use (turbine oil according to Japanese IndustrialStandard) No. 200 Nov 180 N0. I40 R-ll 3g -4 2 38-40 R-l I3 4 45'18-42.. 34- 3 R-l l4 39 -41 These oils having additive material added asabove exhibit performances similar to that of conventional oils inlubrication, cooling, and sealing for the compressor.

A preferred arrangement for carrying out the invention will behereinafter explained by reference to the accompanying drawing.

In FIG. 1, there is shown Conventional oil recovery systems, whereinconventional oil fed to a screw type air compressor 1 serves forlubrication, cooling, and sealing in the compressor and passes through acheck valve 2 and then into an oil separator (or oil recovery device) 3together with the compressed air. The oil separated and recovered fromthe air by the oil separator passes through an oil temperatureregulating valve or an oil cooler 4 and is again fed back to thecompressor by an oil pump 6.

It is noted that in the prior art systems the compressed air containingoil is not cooled yet before passing through the oil separator (toprevent the water from being condensed by cooling, as above mentioned).

The condensed water deposited in the bottom of the oil separator can bedrained through a drain valve 7.

As above mentioned, it is impossible to automatically discharge thecondensed water from the oil separator since the conventional oil has alower specific gravity than water to allow the water to be depositedbelow the layer of oil.

Referring to FIG. 2, there is illustrated a typical system with whichthe present invention is carried out. The additive material is mixedwith the oil to be supplied into the screw type air compressor 1 wherebythe oil exhibits a heavier specific gravity than that of water. The oilhaving the additive material mixed, serves for lubrication, cooling andsealing in the compressor in the same manner as the conventional oil andis discharged with the compressed air through the check valve 2. Thecompressed air with oil is fully cooled in a cooler 4 before the oilseparator (or recovery device) 3. This differs from the prior art systemshown in FIG. 1, as precisely mentioned hereinbefore. The condensedwater and oil are separated from the compressed air by the oil separatorand then distinctly divided into two phases, wherein the oil isdeposited below the layer of 4 water in the oil separator. The oil thusrecovered is again fed back to the compressor by the oil pump 6 whereasthe supernatant water automatically overflows and is discharged throughan auto-drain valve (or overflow discharge valve) 7.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

What I claim is:

1. In a method of operating an air compressor in which lubricating oilhaving a specific gravity lower than that of water is supplied to thecompressor, moisture and entrained oil droplets are discharged from saidcompressor with the compressed air and are removed from said air bycooling said air until moisture is condensed and entrained oil dropletsare precipitated from said air, and the precipitated oil and condensedmoisture are separated by settling, the improvement which comprisesmixing said oil prior to said discharging with an amount of an additivehaving a boiling point at atmospheric pressure higher than the freezingpoint of water and lower than the boiling point of water, said additivebeing more soluble in said oil than in said water, having a specificgravity sufficiently higher than that of said water to raise thespecific gravity of the mixture of said oil with said amount of additiveabove that of water, and a viscosity sufficient to substantiallymaintain the lubricant properties of said oil when added to the same insaid amount, said additive being non-corrosive to machinery and tools,whereby said condensed moisture forms a supernatant on the precipitatedmixture after said cooling.

2. In a method as set forth in claim 1, said additive beingtrichlorofluoromethane, trichlorotrifluoroethane, ordichlorotetrafluoroethane.

3. In a method as set forth in claim 1, said additive beingtrichlorofluoromethane, and being added to said lubricating oil in anamount of 38 percent to 42 percent of the volume of said oil.

4. In a method as set forth in claim 1, said additive beingtrichlorotrifluoroethane, and being added to said lubricating oil in anamount of 34 percent to 45 percent of the volume of said oil.

5. In a method as set forth in claim 1, said additive beingdichlorotetrafluoroethane, and being added to said lubricating oil in anamount of 39 percent to 41 percent of the volume of said oil.

6. In a method as set forth in claim 1, separating said supernatantcondensed moisture from said mixture by overflowing said moisture, andreturning said mixture to said compressor.

7. A method as set forth in claim I, wherein said additive is added tosaid lubricating oil before said lubricating oil is supplied to saidcompressor.

2. In a method as set forth in claim 1, said additive beingtrichlorofluoromethane, trichlorotrifluoroethane, ordichlorotetrafluoroethane.
 3. In a method as set forth in claim 1, saidadditive being trichlorofluoromethane, and being added to saidlubricating oil in an amount of 38 percent to 42 percent of the volumeof said oil.
 4. In a method as set forth in claim 1, said additive beingtrichlorotrifluoroethane, and being added to said lubricating oil in anamount of 34 percent to 45 percent of the volume of said oil.
 5. In amethod as set forth in claim 1, said additive beingdichlorotetrafluoroethane, and being added to said lubricating oil in anamount of 39 percent to 41 percent of the volume of said oil.
 6. In amethod as set forth in claim 1, separating said supernatant condensedmoisture from said mixture by overflowing said moisture, and returningsaid mixture to said compressor.
 7. A method as set forth in claim 1,wherein said additive is added to said lubricating oil before saidlubricating oil is supplied to said compressor.